The present invention relates to a valve operating apparatus for an internal combustion engine. More particularly, the invention involves valve operating apparatus including a sensing device for monitoring the operational condition of the apparatus.
Internal combustion engines are known in which a plurality of intake or exhaust valves are associated with each engine cylinder and wherein valve operating apparatus are effective, during periods of low-speed operation of the engine, to reduce the number of operative valves and, during periods of high speed operation of the engine, to not only effect the operation of all of the valves, but to vary their timing in accordance with engine operating conditions as well. One such arrangement is disclosed in Japanese Laid-Open Patent Publication No. 61-19911, which is assigned to the assignee herein. Such arrangement includes a camshaft rotatable in synchronism with the rotation in an engine. The camshaft has an integral low-speed cam aligned with one of the intake or exhaust valves, which cam has a cam profile corresponding to low-speed operation of the engine. Also included on the cam shaft is an integral high-speed cam having a cam profile corresponding to high-speed operation of the engine. A rocker shaft contains a first rocker arm angularly movably supported on the rocker shaft and held in sliding contact with the low-speed cam and engageable with said one intake or exhaust valve. A second rocker arm is also angularly movably supported on the rocker shaft and engageable with the other intake or exhaust valve, while a third rocker arm is held in sliding contact with the high-speed cam. The first, second and third rocker arms are relatively angularly displaceable in mutual sliding contact, and have coupling means for selectively disconnecting or interconnecting the rocker arms to allow them to either be relatively angularly displaceable or to be angularly displaced in unison. As disclosed in the specification of the above publication, the coupling device includes pistons slidably fitted in mutually communicating guide holes defined in the rocker arms, the pistons being hydraulically operable to interconnect the rocker arms.
In the operation of the above structure, when the base-circle portions of the cams are held in sliding contact with the cam slippers of the rocker arms, the guide holes of the rocker arms are held in registry with each other, and the pistons can be operated in the respective guide holes. However, if, in such structure, the cam slippers of the rocker arms are subjected to abnormal wear, the swinging angles of the rocker arms will be varied and the guide holes may be displaced out of registry, so that the pistons may not be operated properly.
In view of the aforesaid problems of the prior art, it is a primary object of the present invention to provide a device for changing the valve operation timing of an internal combustion engine, the device being capable of reliably detecting the operating condition of the pistons of the coupling means with a relatively simple structure so that corrective measures can be taken rapidly if the pistons fail to operate normally.